Printed circuits and method for making same

ABSTRACT

A method for making printed circuits and printed circuit boards which includes coating a non-metallized substrate and plating an image of a desired circuit design directly onto the coated substrate without the need to image the circuit design on an intermediate silver halide polyester film or diazo and utilizing existing imaging, developing and etching subtractive techniques in conventional printed circuit board processing.

FIELD OF INVENTION

The present invention relates to a printed circuit board technology andmore particularly to a method for making printed circuits which includescoating a non-metallized substrate and plating an image of a circuitdesign directly onto the coated substrate. The present invention alsorelates to printed circuits and printed circuit boards which result fromthis method.

BACKGROUND OF THE INVENTION

Prior art processes for making printed circuits and printed circuitboards typically use a silver halide polyester based film to create animage of a desired printed circuit along with several other steps andprocesses for forming and developing the printed circuit. A photoplotter is a piece of equipment that typically uses silver halidepolyester film as the medium for imaging the design of a circuit. Thisequipment is then used in subsequent processing to image circuits formetallization or to print and etch specifically designed circuits. Thisis known as a print and etch process or a plate and etch process.

One example of a prior art process for forming printed circuit boardsincludes the steps of creating a CAD/CAM design, sending data relatingto the design to a photo plotter, photo plotting to a silver halidepolyester film, developing an image from the sent data, creatingintermediate tools, scrubbing or cleaning substrate for imaging, coatingthe substrate with a dry film, imaging the substrate with the design,developing the image, etching the image, and then stripping theremaining dry film. This prior art process requires several steps andhas limitations on the imaging, developing, and etching of fine lineimages. With this process, fine line imaging can be consistentlyperformed down to 0.003 inches. Imaging of much finer lines, for exampleimaging fine lines down to 0.0025 inches, creates a problem and isinconsistent when using this prior art process. In addition, laminatemust be purchased with copper adhered to a panel and this type ofprocessing has inherent issues with undercutting and rough edges whichcan create “lossy” issues for high speed RF applications. In otherwords, with this process, any rough protrusions or undercutting act likesmall antennas and the signal travel speed is reduced or lost duringhigh frequency applications. High frequency applications require smoothimages and very thin copper.

Accordingly, there is a need for a new method for making printedcircuits and printed circuit boards which facilitate fine line imagingwithout the inherent problem seen in the prior art processes. Inaddition, a method for making printed circuits and printed circuitboards is needed which will eliminate many of the steps used in priorart processes while still enabling the creation of printed circuits andprinted circuit boards with fine line imaging with very flat non-roughsurfaces without undercut utilizing very thin copper below 0.0002.

SUMMARY OF THE INVENTION

The present invention is directed to a method for making printedcircuits and printed circuit boards which eliminates the need for silverfilm used in imaging dry film in prior art processes. The method formaking printed circuits and printed circuit boards in the presentinvention includes the steps of coating a non-metallized substrate andplating an image of the circuit design directly onto the coatedsubstrate. The image substrate can then be developed and processed tocreate a resulting printed circuit without the need for additionalprinting of dry film, developing of dry film and etching processes.

In one exemplary embodiment, the non-metallized substrate may be aliquid crystal polymer, a polyimide, a ceramic, a ceramic filled, aglass, a filled polytetrafluoroethylene, an unfilledpolytetrafluoroethylene, a polytetrafluoroethylene woven glass, and apolytetrafluoroethylene non woven glass which is coated and an image ofthe desired circuit is then plated directly onto the coated substrate.

The present invention is also directed to a printed circuit that is madein accordance with the above-described method where the printed circuitincludes fine line images down to 0.00025 inches with very thin copper.

Another exemplary method of the present invention for making printedcircuits and printed circuit boards includes the steps of providing anon-metallized pre-tooled substrate, coating a surface of the substratewith a photosensitive chemical suitable for laser imaging, baking thecoated substrate until dry, designing circuitry and sending datarelating to the circuitry design to a laser photo plotter or directimaging plotter, imaging the circuitry design directly onto the coatedsubstrate material with the laser photo plotter or direct imagingplotter using the tooling in the coated substrate as a reference for theimaging step, developing the imaged substrate with one or morechemistries, and processing the developed image with a copper bath.

The previously described non-metallized substrates may be used with thismethod and the photosensitive chemicals used to coat the non-metallizedsurface may include a silver nitrate based liquid, a silver chloridebased with citric acid and a photosensitive gelatin, an iron basedmaterial, a chrome copper based material, and a chrome nickel basedmaterial, an immersion gold material, a platinum based material used inconjunction with palladium.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe appended drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 is a flow chart depicting a prior art process for making printedcircuits and printed circuit boards;

FIG. 2 is a flow chart depicting an exemplary embodiment of the methodof the present invention for fabricating printed circuits and printedcircuit boards; and

FIG. 3 is a flow chart depicting another exemplary embodiment of themethod of the present invention for fabricating printed circuits andprinted circuit boards.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Methods of the present invention for fabricating printed circuits andprinted circuit boards generally include providing a non-metallizedsubstrate, coating the non-metallized substrate, and imaging of acircuit design directly onto the coated substrate. The image substratemay then be developed with one or more chemistries and processed bysubjecting it to a copper bath in order to create a printed circuit orprinted circuit board. It should be understood by those skilled in theart that any type of non-metallized substrate may be used as long as thesubstrate is uniform for imaging. In addition, those skilled in the artwill understand that a number of photosensitive chemicals may be used tocoat the surface of the non-metallized substrate and that a variety ofchemistries may be used to develop the imaged substrate.

FIG. 1 shows a flow chart 10 which depicts a prior art process forforming printed circuits and printed circuit boards. In step 12, acircuit is created with a CAD/CAM design and the data relating to thecircuit design is sent to a photo plotter in step 14. Next, in step 16,the circuit design is photo plotted to a silver halide polyester filmand the image on the silver halide polyester film is then developed instep 18. Intermediate tools are created in step 20. A substrate, such asa liquid crystal polymer or a polytetrafluoroethylene is then scrubbedor cleaned in step 22 to ready it for imaging. The substrate is thencoated with a dry film in step 24 and the substrate is imaged with thecircuit design in step 26. Following imaging of the printed circuit onthe coated substrate, the image of the printed circuit is developed instep 28. The developed image of the printed circuit on the coatedsubstrate is then etched in step 30 and any remaining dry film isstripped away in step 32 in order to create a printed circuit.

Turning now to FIG. 2, flow chart 20 is shown which depicts an exemplaryembodiment of the method of the present invention for fabricating aprinted circuit or printed circuit board. First, a non-metallizedsubstrate is coated in step 21. Then, in step 22, a circuit design iscreated. The data relating to the circuit design is then sent to a photoplotter or direct imaging equipment in step 24 and the image relating tothe circuit design is directly plotted on the coated non-metallizedsubstrate in step 26. Unlike prior art processes, the image is notplotted to an intermediate silver halide polyester film or diazo. Theplotted or direct image of the circuit design is then developed in step28 and the developed image is then processed in step 30 without the needfor intermediate developing and etching processes.

Another, more detailed exemplary embodiment of the present invention forfabricating printed circuits and printed circuit boards is shown in FIG.3 by flow chart 50. First, a non-metallized pre-tooled substrate isprovided in step 48 which is then coated in step 51. The non-metallizedpre-tooled substrate may comprise any substrate or bonding film known inthe industry of printed circuit board technology as long as thesubstrate is flat and uniform for imaging. For example, thenon-metallized substrate may be a liquid crystal polymer, a polyimide, aflat glass plate, a polyethylene terephthalate, a filledpolytetrafluoroethylene, a unfilled polytetrafluoroethylene, apolytetrafluoroethylene woven glass, a polytetrafluoroethylene non wovenglass, a low temperature cofired ceramic (LTCC), and a high temperaturecofired ceramic (HTCC). The substrates may be woven or non woven andceramic filled or unfilled. In addition, a number of known products mayalso be used as the non-metallized substrate including products known asKAPTON, SPEED BOARD C, ULTRALAM, FR4 EPOXIES, MULTIFUNCTIONAL EPOXIES,BT EPOXIES, LCP, and DUROID. The non-metallized pre-tooled substrate iscoated in step 51 with a photosensitive chemical that is suitable forlaser imaging. Such chemicals may include, but are not limited to, asilver nitrate based liquid, a silver chloride based with citric acidand photosensitive gelatin, an iron based material, a chrome copperbased material, and a chrome nickel based material, electroless nickel,immersion gold, platinum based and palladium based material.

The coated substrate is then baked until dry in step 49. In oneexemplary embodiment, the coated substrate is baked at 40 degreesCelsius in a conventional oven or a conveyor oven for approximately 20to 30 minutes. The circuitry for the printed circuit or printed circuitboard is then designed in step 52 and the data relating to the circuitdesign is sent to a photo plotter or laser direct imaging in step 54.Next, the circuitry design is imaged onto the coated substrate using thephoto plotter or laser direct imager in step 56 and the tooling in thecoated substrate is used as a reference guide during the imaging. Incontrast to prior art processes, a silver halide polyester film is notused for imaging. Instead, the coated substrate is placed directly onthe photo plotter or laser direct imager for imaging. As a result, themethod of the present invention for fabricating printed circuits andprinted circuit boards eliminates the need for a number of products,steps, and procedures including the need for silver film, diazo film,dry film, liquid dry films, collimated or non-collimated UV lightsources, hot roll vacuum lamination, developing and etching andstripping of standard printed circuit boards, and waste treatmentchemicals along with associated overhead and direct and indirect laborcosts.

In the exemplary method shown in FIG. 3, the image substrate is thendeveloped with chemistries in step 58. Here, chemistries such as anypaper type developer like KODAK DEKTOL or NGS NAT 540 and FIXER NAT 750may be used or EDTA based developer. Finally, the developed image isprocessed in step 60 with a copper bath to create the resulting printedcircuit or printed circuit board. This may include any standardelectroless copper plating process used for circuit board holemetallization that is known in the art.

It will be understood that the foregoing description is of preferredexemplary embodiments of the invention and that the invention is notlimited to specific forms shown or described herein. Variousmodifications may be made in the design, arrangement, order, and typesof steps disclosed herein for making and using the invention withoutdeparting from the scope of the invention as expressed in the appendedclaims.

1. A method for making a printed circuit comprising coating anon-metallized substrate and plating an image of a circuit designdirectly onto the coated substrate.
 2. The method of claim 1 furthercomprising the steps of developing the imaged substrate and processingthe developed image by subjecting the imaged substrate to a copper bath.3. The method of claim 1 wherein the non-metallized substrate comprisesat least one of a liquid crystal polymer, a polyimide, a polyethyleneterephthalate, a filled polytetrafluoroethylene, an unfilledpolytetrafluoroethylene, a polytetrafluoroethylene woven glass, apolytetrafluoroethylene non woven glass, a low temperature cofiredceramic, and a high temperature cofired ceramic.
 4. The method of claim1 wherein the non-metallized substrate comprises at least one of theproducts known as LCP, KAPTON, SPEED BOARD C, PET, ULTRALAM, and DUROID.5. A printed circuit made in accordance with the method of claim
 1. 6.The printed circuit board of claim 5 wherein the printed circuitcomprises fine line images down to 0.00025 inches.
 7. A method formaking printed circuit boards comprising: providing a non-metallizedpre-tooled substrate; coating a surface of the substrate with aphotosensitive chemical suitable for laser imaging; baking the coatedsubstrate until dry; designing circuitry and sending data relating tothe circuitry design to a photo plotter; imaging the circuitry designdirectly onto the coated substrate material with the photo plotter usingthe tooling in the coated substrate as a reference for the imaging step;developing the imaged substrate with one or more chemistries; andprocessing the developed image with a copper bath.
 8. The method ofclaim 8 wherein the non-metallized pre-tooled substrate comprises atleast one of a liquid crystal polymer, a polyimide, a polyethyleneterephthalate, a filled polytetrafluoroethylene, an unfilledpolytetrafluoroethylene, a polytetrafluoroethylene woven glass, apolytetrafluoroethylene non woven glass, a low temperature cofiredceramic, and a high temperature cofired ceramic.
 9. The method of claim8 wherein the non-metallized pre-tooled substrate comprises at least oneof the products known as LCP, KAPTON, SPEED BOARD C, PET, ULTRALAM, andDUROID.
 10. The method of claim 8 wherein the photosensitive chemicalused to coat the non-metallized surface comprises one of a silvernitrate based liquid, a silver chloride based with citric acid and aphotosensitive gelatin, an iron based material, a chrome copper basedmaterial, and a chrome nickel based material.
 11. The method of claim 8wherein the coated substrate is baked at 40 degrees C. in a conventionaloven or a conveyor oven.
 12. The method of claim 8 wherein thechemistries used to develop the imaged substrate comprise any chemistryused to develop an image on paper.
 13. The method of claim 8 whereinprocessing the developed image in a copper bath results in metallizingthe image left after photo plotting.
 14. The method of claim 8 whereinthe imaging step comprises imaging fine lines down to 0.00025 inches.15. A printed circuit board made in accordance with the method of claim8.
 16. The printed circuit board of claim 15 wherein the printed circuitcomprises fine line images down to 0.00025 inches.